Method of manufacturing fuse elements from strip material for cartridge fuse links



March 18, 1969 .1 FEENAN ET AL METHOD OF MANUFACTURING FUSE ELEMENTSFROM STRIP MATERIAL FOR CARTRIDGE FUSE LINKS Original Filed Jan. 30,1964 APPLICANTS John Feenan, Eric Jacks and John Eric Murphy BYMisegades 80 Douglas ATTORNEYS United States Patent Office 5,145 63 US.Cl. 29-623 2 Claims Int. Cl. H01h 6'9/02 ABSTRACT OF THE DISCLOSURE Thisinvention relates to a method of forming a fuse element from stripmaterial by initially rolling in the strip a plurality of grooves spacedapart along its length and subsequently forming notches on oppositesides of the strip along the length of each groove, whereby thethickness and width of each neck portion thus produced are less than thethickness and width of the remaining portions of the strip adjacentthereto.

This application is a division of our co-pending application Ser. No.341,267 filed on Jan. 30, 1964, now Patent No. 3,288,968.

The invention relates to electrical fuse-elements and is particularlyapplicable to fuse-elements for use in cartridge fuse links of the typein which a fuse-element is supported within a tubular insulatingcontainer by two conductive members secured to the container one at eachend thereof.

According to the invention, there is provided a method of producing afuse element from a strip of fusible metal, comprising the steps ofinitially forming a groove across the width of the strip andsubsequently forming notches on opposite sides of the strip along thelength of the groove, whereby the thickness and width of the neckportion so formed are less than the thickness and width of the remainingportion of the strip.

A preferred form of fuse-element made by a method according to thisinvention will now be described with reference to the accompanyingdrawings in which:

FIG. 1 is a perspective view of the fuse-element; and

FIG. 2 is a fragmentary view, to an enlarged scale, of part of thefuse-element.

The fuse-element comprises a strip 10 of silver which is provided with aseries of neck portions 11 joining fullsection portions such as thoseindicated at 12. The neck portions 11 are disposed centrally relative tothe width of the strip 10 and have a thickness x (FIG. 2) which is lessthan the thickness v of the full-section portions 12. Thecross-sectional area of each neck portion 11 in the plane perpendicularto the length of the strip 10 is approximately the cross-sectional areaof each fullsection portion 12.

The fuse-element includes a thickened portion 13 for reducing theoverall resistance of the fuse. Such a portion may be positioned ateither or both ends of the element and/ or in the middle of the element.

In producing this fuse element, the appropriate strip of material is fedbetween two closely spaced contrarotating rollers, one having a planesurface and the other having a male contour conforming to the grooves tobe formed in the strip, the clear spacing between the rollers thusdefining the thickness of the neck portion slots are then formed,extending inwardly from the ends of the groove so as to define thelateral width of the neck por- 3,432,923 Patented Mar. 18, 1969 tion.Alternatively, the grooves can be formed by milling with a cutter.

It has been found that a ratio between the cross-sectional areas of thefull-section portions and the neck portion of the order of 10:1 (thatis, ranging from about 8:1 to about 12:1), as in this case, is animportant factor in producing a fuse with a high current rating withinlimited dimensions and with a fast fusing action. It has also been foundthat the proportions of the neck portion affect the distribution ofcurrent in the full-section portions and hence the overall effectiveresistance of the fuse element which should be as low as possible. Thebest current distribution in the full-section portions (and hence thelowest overall effective resistance) is obtained by reducing thethickness, rather than the width, of the neck portion: ideally, the neckportion would consist of a groove extending across the whole width ofthe strip. However, the desired ratio of cross-sectional areas betweenthe full-section portions and the neck portion cannot in many cases beobtained in this way without so reducing the thickness of the strip atthe groove as to make the strip unmanageable mechanically. Therefore, byproviding, in a fuse-element according to the invention, a neck-portionhaving both a reduced width and a reduced thickness, a compromise can bemade between the conflicting requirements of mechanical strength andgood current distribution and at the same time the desired ratio ofcross-sectional areas can be achieved. In a test illustrating this, afirst fuse-element, three inches long was provided, with a series of sixneck portions by simply forming slots in the sides of the strip so thatthe lateral width of the strip was reduced to of the full width. Themeasured resistance was 750 microhms. A second fuse-element of the samelength had the thickness of the neck portions reduced from .010 inchi.e. about 1:3, to 0.003 inches enabling the width of the neck portionsto be 3 /3 times wider than in the first fuseelement for the samecross-sectional area. The measured resistance of the second element was600 microhms.

Desirably, the required cross-sectional area of the neck portion shouldbe spread over as much of the width of the strip as possiblecommensurate with good mechanical strength: this also provides the mosteffective heat dissipation because, for a given cross-section, thelargest possible surface area is available for heat transfer pur poses.

What we claim as our invention and desire to secure by Letters Patentis:

1. A method of producing a fuse element from a strip of fusible metalsubstantially rectangular in cross-section, comprising the steps ofinitially forming across the width of the strip a plurality of groovesspaced apart along the length of the strip so that the thickness of thestrip in the grooves is reduced to about one-third, and

subsequently forming notches of equal length on opposite sides of thestrip along the length of each groove, whereby both the thickness andthe width of each neck portion thus produced are less than the thicknessand width of the remaining portions of the strip.

2. A method of producing a fuse element from a strip of fusible metalsubstantially rectangular in crosssection, comprising the steps ofinitially forming a plurality of grooves extending across the width ofthe strip by a rolling operation, the grooves being spaced apart alongthe length of the strip so that the thickness of the strip in thegrooves is reduced to about one-third, and

subsequently forming notches of equal length on 0pposite sides of thestrip along the length of each 1,973,120 9/1934 Steinmayer -1 2001352,157,906 5/1939 Lohausen 200-135 X 2,157,907 5/ 1939 Lohausen.

Alberla et a1. 200135 X Horrer 72-203 Cremer 200135 X Lear 200135 5 JOHNF. CAMPBELL, Primary Examiner.

J. L. CLINE, Assistant Examiner.

US. Cl. X.R.

